The invention is directed to a liquid filter, particularly for oil or fuel of an internal combustion engine, whereby the liquid filter comprises a filter housing having at least one respective liquid intake channel and liquid return channel, a detachable cover that closes the filter housing liquid-tight, and a filter insert that can be removed from the filter housing and can be individually replaced, and whereby the liquid filter can be screwed to a filter connecting flange of, for example, an internal combustion engine in sealing fashion instead of a screw-on replaceable filter that can only be replaced as a complete unit.
Screw-on replaceable filters are known and widespread and have been utilized for many years, particularly in connection with the internal combustion engines of motor vehicles. What has proven disadvantageous a bout these screw-on replacement filters is that the complete replacement filter must be disposed of with every replacement, this leading to substantial quantities of waste and to a great waste of material.
In order to alleviate these disadvantages, different liquid filters have already been proposed for a refitting or after-fitting as replacement for traditional screw-on replacement filters, whereby only a filter insert need be replaced and the remaining part of the liquid filter is re-employable.
A first liquid filter of the type first described above is disclosed by DE 40 36 191 A1. Given this known filter, the complete filter is first unscrewed from the appertaining internal combustion engine for a replacement of the filter insert. Subsequently, the filter housing can be opened and the used filter cartridge can be removed and be replaced by a new filter cartridge. After this, the filter housing is reassembled or, respectively, closed again and is then screwed back onto the internal combustion engine. For connecting this filter to the internal combustion engine, the filter housing comprises a head plate at the face side that is implemented of one piece with a central arbor having an inside thread. This arbor having the inside thread can be screwed onto a mating connector element with outside thread at the internal combustion engine, whereby the required flow connections between the internal combustion engine and filter, while being sealed from the outside, are produced at the same time.
What is considered disadvantageous in this known filter is that a high disassembly and assembly outlay is required for changing the filter cartridge, this leading to a high time outlay and to an increased risk of assembly errors.
Another liquid filter of the type first described is disclosed by DE 42 01 041 A1. A filter housing is provided in this filter that is formed of one piece with a wall of the face side and with a tubular connecting piece with inside thread that is centrally arranged therein and projects into the inside of the filter. The filter housing can be closed at its other end with a screw-on cover, whereby the screw-on cover can be unscrewed from the filter housing for the purpose of replacing the filter insert. The filter housing can thereby remain at the motor block of the internal combustion engine.
Finally, DE 42 40 656 A1 discloses a filter that likewise comprises a base plate at the face side that has an attachment with inside thread that is formed of one piece therewith and points toward the inside into the filter housing. Here, too, a cover of the filter housing can be screwed off for the purpose of replacing the filter insert. A drain plug is also provided in the center of the cover given this known filter, this serving the purpose of draining the filter housing before a replacement of the filter insert. This draining, however, disadvantageously only functions when the filter is built in "hanging", i.e. having an essentially vertical longitudinal axis with the cover pointing in downward direction. Given a horizonal installed attitude, for example, the filter housing can be at most approximately half empty given such a drain plug.
Further, all known filters set forth above have the disadvantage that their ultimate position, viewed in circumferential direction in their screwed-on condition, is completely arbitrary, since this defined only by the relative position of the threads of the inside and the outside threads of the screw-type connection. As a result thereof, for example, filter housings cannot be employed that have their circumference equipped with a drain opening for emptying the filter housing, since it cannot be assured that the drain opening, given a horizonal or approximately horizontal arrangement of the filter, in fact points downward or at least approximately downward in the screwed-on condition of the filter.
Finally, it is also to be considered disadvantageous that the seal ring arranged between filter housing and filter connecting flange in all known filters of the type first described, wherein the filter housing can be turned as a unit for being screwed to the filter connecting flange, is subjected to substantial stresses in circumferential direction. Even given a careful mounting and prior oiling or lubricating of the seal ring, it can easily occur that the seal ring is distorted or is displaced out of its intended position when the filter housing is screwed on, this involving a relatively high risk of leaks that arise either due to the incorrect position of the seal ring or due to damage thereof during the screw-on event.
The need therefore arises of creating a liquid filter of the type first described that avoids the disadvantages recited above and whereby a freely selectable position in the screwed-on condition is assured as viewed in circumferential direction and whereby the risk of leaks is reduced.